1. Field of the Invention
The present invention relates to an image blur preventing device for preventing image blur resulting, for example, from hand vibration in a camera, an optical instrument or the like.
2. Related Background Art
In recent cameras, the possibility of failure in photograph taking is quite low even for an amateur who is not skilled in the manipulation of the camera, because important operations for photograph taking such as determination of the exposure and focusing are all automated.
Also, systems have been developed for preventing interference of hand vibration to the camera, so that few factors inducing the failure in photograph taking are left on the part of the photographer.
In the following there will be briefly explained such system for preventing hand vibration.
Vibration of the camera induced by hand vibration during photograph taking usually has a frequency of 1 to 12 Hz. The basic principle for providing a photograph without image blur even in the presence of such hand vibration when the shutter is released consists of detecting the vibration of the camera induced by such hand vibration and displacing a correction lens in response to the detected amount. Therefore, in order to obtain a photograph without image blur even in the presence of a camera vibration, it is necessary to first precisely detect the vibration of the camera and then to correct the change in the optical axis resulting from such vibration.
The detection of such vibration (camera vibration) can in principle be achieved by providing the camera with vibration detection means (e.g., a sensor) for detecting an angular acceleration, an angular velocity or an angular variation, and camera vibration detection means for outputting the angular variation by electrically or mechanically integrating the output signal of the sensor. The image vibration can be suppressed by driving a correcting optical device, for deviating the photographing optical axis, based on the detected information.
A vibration preventing system employing such a vibration detection means now is described with reference to FIG. 18.
FIG. 18 shows a system for suppressing the image blur resulting from a pitching vibration 81p and a yawing vibration 81y of the camera, indicated by arrows 81.
In FIG. 18, there are shown a lens barrel 82; vibration detection means 83p, 83y for respectively detecting pitching and yawing vibrations of the camera, with respective vibration detecting directions 84p, 84y; and an optical correction device 85 (with coils 87p, 87y for applying driving forces to the optical correction device 85 and position detectors 86p, 86y for detecting the position of correction device 85). The optical correction device 85 is provided with a position control loop to be explained later, and is driven with the outputs of the vibration detection means 83p, 83y as target values thereby achieving stabilization on the image plane 88.
FIG. 19 is an exploded perspective view of an image blur correction device (composed of the above-mentioned vibration detection means, optical correction device, coils, position detectors and various IC's to be explained later) adapted for use for the above-mentioned object. The structure of this device will be explained with reference to FIGS. 19 to 28.
A base plate 71 (shown in FIG. 22 in magnified manner) is provided with three rear projections 71a (one being not visible) which are fitted on an unrepresented lens barrel, and are fixed thereto by screwing of known lens barrel rollers or the like into holes 71b.
A second yoke 72, composed of a magnetic material and provided with metal plating is fixed to holes 71c of the base plate 71 by screws passing through holes 72a. Permanent magnets (shifting magnets) 73 such as neodymium magnets are magnetically adhered to the second yoke 72. The permanent magnets 73 are respectively magnetized in directions indicated by arrows 73a shown in FIG. 19.
In a support frame 75 (shown in FIG. 23 in magnified manner), in which a correction lens 74 is fixed with C-rings or the like, coils (shifting coils) 76p, 76y are fixed by forced fitting (FIG. 23 showing an unfixed state), and light emitting elements 77p, 77y such as IRED's are also adhered to the rear face of the support frame 75, whereby the emitted lights pass through slits 75ap, 75ay and enter position detecting elements 78p, 78y such as PSD's to be explained later.
In three holes 75b of the support frame 75, there are inserted support balls 79a, 79b with spherical ends, composed for example of POM (polyacetal resin), and charging springs 710 (cf. FIGS. 20 and 21A), and the support balls 79a are fixed to the support frame 75 by heat caulking (support balls 79b being rendered slidable in the direction of holes 75b, against the force of the charging springs 710).
FIG. 20 is a longitudinal cross-sectional view of the image vibration correction device after assembling thereof. In each hole 75b of the support frame 75, there are inserted in succession, in a direction 79c, the support ball 79b, the charged spring 710 and the support ball 79a (support balls 79a and 79b being identical in shape), and the peripheral edge 75c of the hole 75b is finally heat caulked to retain the support ball 79a.
FIG. 21A is a cross-sectional view of the hole 75b in a direction perpendicular to the plane of FIG. 20, and FIG. 21B is a plan view of the hole 75b seen from a direction 79c. In FIG. 21A, symbols A to D indicate depths of areas A to D shown in FIG. 21B.
As the rear end of a fin portion 79aa of the support ball 79a is received and limited by an area of the depth A, the support ball 79a is fixed to the support frame 75 by the heat caulking of the peripheral edge 75a.
Also as the front end of a fin portion 79ba of the support ball 79b is received and limited by an area of the depth B, the support ball 79b cannot escape, under the force of the charging spring 710, from the hole 75b in a direction 79c.
After the assembling of the image blur correcting device, the support ball 79b is received by the second yoke 72 as shown in FIG. 20 and cannot escape from the support frame 75, but the escape preventing area B is provided in consideration of convenience of assembling.
As the shape of the hole 75b of the support frame 75, as illustrated in FIGS. 20, 21A and 21B, does not require, in the molding of the support frame 75, a complex mold but can be prepared with a simple two-part mold in which a part is extracted in a direction opposite to the arrow 79c, so that the dimensional precision can be strictly defined.
Also as the support balls 79a, 79b are identical in shape, it is rendered possible to reduce the cost of the parts, to avoid errors in assembling and to facilitate management of the parts.
In a bearing portion 75d of the support frame 75, there is coated for example fluorinated grease, and an L-shaped shaft 711 (made of non-magnetic stainless steel) is inserted therein (cf. FIG. 19). The other end of the L-shaped shaft 711 is inserted into a bearing portion 71d (similarly coated with grease) of the base plate 71, and the support frame 75 is placed in the base plate 71, with three support balls 79b riding on the second yoke 72.
Then three positioning holes 712a of a first yoke 712 shown in FIG. 19 are fitted on three pins 71f, shown in FIG. 22, of the base plate 71, and the first yoke 712 is received by five receiving faces 71e, shown in FIG. 22, and is magnetically coupled, by the magnetic force of the magnets 73, to the base plate 71.
In this manner the rear face of the first yoke 712 comes into contact with the support balls 79a, and, as shown in FIG. 20, the support frame 75 is sandwiched between the first yoke 712 and the second yoke 72 and is defined in position in the axial direction.
Fluorinated grease is also coated in the contact portions between the support balls 79a, 79b and the first and second yokes 712, 72 so that the support frame 75 is rendered freely slidable with respect to the base plate 71, in a plane perpendicular to the optical axis.
The L-shaped shaft 711 supports the support frame 75 so as to be slidable only in the directions 713p, 713y with respect to the base plate 71, whereby the support frame 75 is prevented from rotation (rolling) about the optical axis with respect to the base plate 71.
The L-shaped shaft 711 has a large fitting play with the bearing portions 71d, 75d in the axial direction, thereby avoiding interference with the limitation in the axial direction by sandwiched supporting by the support balls 79a, 79b and the first and second yokes 712, 72.
On the surface of the first yoke 712 there is provided an insulating sheet 714, on which a hard circuit board 715 with plural IC's (position detectors 78p, 78y, an output amplifying IC, coils 76p, 76y, a driving IC etc.) is fixed by fitting two positioning holes 715a thereof on two pins 71h of the base plate 71, shown in FIG. 22, fitting screws through holes 715b, holes 712b of the first yoke 712 and holes 71g of the base plate 71.
On the hard circuit board 715, the position detectors 78p, 78y are positioned with a jig and soldered, and a signal transmitting flexible circuit board 716 is also attached to the rear face of the hard circuit board 715 by heat pressing a face 716a of the flexible board 716 to a broken-lined area 715c (cf. FIG. 19).
From the flexible circuit board 716, there extend a pair of arms 716bp, 716by in a plane perpendicular to the optical axis, and respectively engage with hooking portions 75ep, 75ey of the support frame 75 (cf. FIG. 23), and the terminals of the light emitting elements 77p, 77y and those of the coils 76p, 76y are soldered thereto.
Thus the light emitting elements 77p, 77y such as IRED's and the coils 76p, 76y are driven by the hard circuit board 715 through the flexible circuit board 716.
The arms 716bp, 716by of the flexible circuit board 716 are respectively provided with bent portions 716cp, 716cy (cf. FIG. 19), and the elasticity of such bent portions reduces the load of the arms 716bp, 716by when the support frame 75 moves in a plane perpendicular to the optical axis.
The first yoke 712 is provided with a molded protruding face 712c, which passes through a hole 714a of the insulating sheet 714 and is in direct contact with the hard circuit board 715. The hard circuit board 715 is provided, on the contact face thereof, with a ground pattern, so that the first yoke 712 is grounded by screwing the hard circuit board 715 to the base plate and is thus prevented from functioning as an antenna which generates and transmits noise to the hard circuit board 715.
A mask 717 shown in FIG. 19 is positioned by pins 71h of the base plate 71 and is adhered, by a double-stick tape, to the hard circuit board 715.
The base plate 71 is provided with a hole 71i for passing the permanent magnet (cf. FIGS. 19 and 22), through which the rear face of the second yoke 72 is exposed. A permanent magnet (locking magnet) 718 is fitted in this hole 71i and is magnetically coupled with the second yoke 72 (cf. FIG. 20).
A locking ring 719 (cf. FIGS. 19, 20 and 24) is provided with a coil (locking coil) 720 adhered thereto, and, behind an ear portion 719a of the locking ring 719 there is provided a bearing 719b (cf. FIG. 25). An armature pin 721 (cf. FIGS. 19 and 25) passes through in succession an armature-rubber 722, the bearing 719b and an armature spring 723 and is fitted in and fixed to an armature 724 by caulking.
Consequently the armature 724 can slide in a direction 725 with respect to the locking ring 719, against the charging force of the armature spring 723.
FIG. 25 is a plan view showing the vibration correcting device in assembled state, seen from the rear side of FIG. 22. The locking ring 719 is mounted to the base plate 71 by known bayonet coupling by fitting three external recesses 719c of the locking ring 719 with three internal projections 71j of the base plate 71, thus pressing the locking ring 719 into the base plate 71 in this state and then rotating the locking ring 719 in the clockwise direction.
Consequently the locking ring 719 is rotatable about the optical axis, with respect to the base plate 71. In order to prevent de-coupling of the bayonet coupling by the rotation of the locking ring 719 to a position where the recesses 719c thereof match the projections 71j, a locking rubber 726 (cf. FIGS. 19 and 25) is pressed into the base plate 71 in such a manner that the locking ring 719 can only rotate by an angle .theta. of a notch 719d (cf. FIG. 25) which is limited by the locking rubber 726.
A magnetic locking yoke 727 (FIG. 19) is also provided with a permanent magnet (locking magnet) 718. Two holes 727a of the locking yoke are fitted with pins 71k (cf. FIG. 25) of the base plate 71, and screw couplings are made through two holes 727b and two holes 71n.
The permanent magnet 718 at the side of the base plate 71, the permanent magnet 718 at the side of the locking yoke 727, the second yoke 72 and the locking yoke 727 constitute a known closed magnetic circuit.
The locking rubber 726 mentioned above is retained in position by the screw coupling of the locking yoke 727. In FIG. 25, the locking yoke 727 is omitted for the purpose of clarity.
Between a hook 719e of the locking ring 719 and a hook 71m of the base plate 71 there is provided a locking spring 728 (cf. FIG. 25) thereby biasing the locking ring 719 clockwise. An attracting yoke 729 (cf. FIGS. 19 and 25) is provided with an attracting coil 730 and is screw coupled, by a hole 729a, with the base plate 71.
The terminals of the coil 720 and those of the attracting coil 730 are composed, for example, of teflon-coated twisted paired wires which are soldered to an end portion 716d of the flexible circuit board 716.
IC's 731p, 731y (cf. FIG. 19) provided on the hard circuit board 715 and serving to amplify the outputs of the position detectors 78p, 78y have an internal structure shown in FIG. 26, which only illustrates the structure of the IC 731p because IC's 731p, 731y have identical structure.
Referring to FIG. 26, current-voltage converting amplifiers 731ap, 731bp respectively convert the photocurrents 78i1p, 78i2p, which are generated in the position detector 78p (consisting of resistors R1, R2) by the light from the light emitting element 77p, into voltages, and a differential amplifier 731cp amplifies the difference of the outputs of the current-voltage converting amplifiers 731ap, 731bp.
The light emitted from the light emitting elements 77p, 77y is transmitted by slits 75ap, 75ay and enters the position detectors 78p, 78y as explained before, and the light entry positions thereto vary if the support frame 75 moves in a plane perpendicular to the optical axis.
The position detector 78p has sensitivity in a direction 78ap (cf. FIG. 19) while the slit 75ap is shaped so as to expand the light beam in a direction 78ay perpendicular to the arrow 78ap but limit the light beam in the direction 78ap. Consequently, the balance of the photocurrents 78i1p and 7812p varies only when the support frame 75 moves in a direction 713p, so that the differential amplifier 731cp generates an output corresponding to the position of the support frame 75 in the direction 713p.
Also the position detector 78y has sensitivity in a direction 78ay (cf. FIG. 19) while the slit 75ay is extended in a direction 78ap perpendicular to the arrow 78ay, so that the output of the position detector 78y varies only when the support frame 75 moves in a direction 713y.
An adding amplifier 731dp determines the sum of the outputs of the current-voltage converting amplifiers 731ap, 731bp (namely the total amount of light received by the position detector 78p), and a driving amplifier 731ep receiving such sum drives the light emitting element 77p accordingly.
The amount of light emitted by the light emitting element 77p fluctuates unstably , e.g., with temperature changes, thus the absolute value (78i1p+78i2p) of the photocurrents 78i1p, 78i2p from the position detector 78p also varies. For this reason, the output (78i1p-78i2p) of the differential amplifier 731cp, indicating the position of the support frame 75, also varies.
However, the fluctuation in the output of the differential amplifier 731cp can be canceled by controlling the light emitting element 77p by the above-mentioned driving circuit in the above-explained manner, such that the sum of the received light is maintained constant.
The coils 76p, 76y shown in FIG. 19 are positioned in the closed magnetic circuit constituted by the permanent magnets 73, the first yoke 712 and the second yoke 72, and a current supply to the coil 76p drives the support frame 75 in a direction 713p (according to the known Flemming's left hand rule) while a current supply to the coil 76y drives the support frame 75 in a direction 713y.
Thus, by driving coils 76p, 76y with the outputs of the position detectors 78p, 78y amplified by the IC's 731p, 731y, the support frame 75 is driven to vary the outputs of the position detectors 78p, 78y.
By selecting the driving directions (polarities) of the coils 76p, 76y so as to reduce the outputs of the position detectors 78p, 78y (negative feedback), the support frame 75 is stabilized by the driving forces of the coils 76p, 76y at a position where the outputs of the position detectors 78p, 78y become substantially zero.
Such a driving method by negative feedback of the outputs of the position detectors is called a position control method, and the support frame 75 can be quite faithfully driven according to a target value (for example an angular signal of hand vibration) supplied to the IC's 731p, 731y from the outside.
In practice, the outputs of the differential amplifiers 731cp, 731cy are supplied through the flexible circuit board 716 to a main board (not shown), and, after A/D conversion, stored in memory in a microcomputer.
In the microcomputer, these signals are compared with target values (hand vibration angular signal), amplified, then subjected to known phase advancement compensation according to a known digital filtering method (for stabilizing the position control), then supplied again through the flexible circuit board 716 to the IC 732 for driving the coils 76p, 76y. The IC 732 executes known PWM (pulse width modulation) drive of the coils 76p, 76y based on the entered signals, thereby driving the support frame 75.
The support frame 75 is freely slidable in directions 713p, 713y as explained before and is stabilized in position by the aforementioned position control method, but, in consumer equipment such as a camera, constant drive of the support frame 75 is not possible when the consumption of power supply is considered. However, the support frame 75 is freely movable in the uncontrolled state in the plane perpendicular to the optical axis, and may collide with the end of the structurally movable range (hereinafter called stroke limit position). This may generate noise or cause damage, and a countermeasure against such free movement must be provided.
For this purpose a locking mechanism for locking the support frame 75 is provided as will be explained in the following.
As shown in FIGS. 25, 27A and 27B, the support frame 75 is provided on the rear face thereof with three radial projections 75f, an end of each projection 75f fits into a respective internal periphery 719g of the locking ring 719 as shown in FIGS. 27A and 27B. Consequently the support frame 75 is restricted in all directions with respect to the base plate 71.
FIGS. 27A and 27B are plan views showing the functional relationship of the locking ring 719 and the support frame 75, showing only principal components extracted from FIG. 25. For the purpose of clarity, the layout is made somewhat different from the actual assembled state. In FIG. 27A, three cam portions 719f are in fact not provided over the entire cylindrical generatrix of the locking ring 719 as shown in FIGS. 20 and 24 and are therefore not visible in the direction of FIG. 25, but they are illustrated for the ease of understanding.
As shown in FIG. 20, the coil 720 (including twisted lead wires 720a in FIGS. 27A and 27B, passing along the external periphery of the locking ring 719 by a flexible circuit board (not shown) and connected from terminal 719h to terminals 716e on a shaft portion 716d of the flexible circuit board 716) is maintained in a closed magnetic circuit between the permanent magnets 718, and, upon receiving a current supply, generates a torque for rotating the locking ring 719 about the optical axis.
The coil 720 is controlled by an instruction signal supplied from a microcomputer (not shown) to the driving IC 733 on the hard circuit board 715 through the flexible circuit board 716 and is PWM driven by the IC 733.
Referring to FIG. 27A, the winding direction of the coil 720 is selected so that, upon energization thereof, an anticlockwise torque is generated in the locking ring 719, whereby the locking ring 719 rotates anticlockwise against the force of the locking spring 728.
Prior to energization of the coil 720, the locking ring 719 is stabilized in contact with the locking rubber 726 under the force of the locking spring 728.
When the locking ring 719 rotates, the armature 724 comes into contact with the attracting yoke 729 to compress the armature spring 723, thereby equalizing the positional relationship of the attracting yoke 729 and the armature 724 and thus stopping the rotation of the locking ring 719, as shown in FIG. 27B.
FIG. 28 is a timing chart of the locking ring drive operation.
At 719i in FIG. 28, the coil 720 is energized (PWM drive indicated by 720b) and the attracting coil magnet 730 is simultaneously energized (730a). Thus the armature 724 comes into contact with the attracting yoke 729, and, at the state of equalization, the armature 724 is attracted by the attracting yoke 729.
Then the coil 720 is deactivated at 720c in FIG. 28 whereupon the locking ring 719 tends to rotate clockwise by the force of the locking spring 728, but such rotation is restricted because the armature 724 is attracted by the attracting yoke 729 as mentioned above. In this state, the projection 75f of the support frame 75 opposes the cam portion 719f (by the rotation thereof), whereby the support frame 75 is rendered movable by an amount corresponding to a clearance between the projection 75f and the cam portion 719f.
Consequently the support frame 75 tends to drop in the direction of gravity (cf. FIG. 27B), but such drop is prevented because movement of the support frame 75 is also controlled at 719i in FIG. 28.
The support frame 75 in the uncontrolled state is restricted inside the internal periphery of the locking ring 719, but in fact has a play corresponding to the fitting play between the projection 75f and the internal peripheral wall 719g. Consequently the support frame 75 tends to drop in the direction of gravity by the amount of such play so that the center of the support frame 75 is displaced from that of the base plate 71. For this reason, there is executed a control of slow movement to the center of the base plate 71, for example, within a one second period from 719i (see FIG. 28).
Such slow movement is adopted because an unpleasant image vibration is perceived by the photographer in the case of a rapid movement to the center, and also in order to avoid deterioration of the image resulting from movement of the support frame 75 during an exposure operation executed in the course of such movement. Such slow movement is executed, for example, by moving the support frame 75 by 5 pm within 1/8 seconds.
More specifically, the outputs of the position detectors 78p, 78y at 719i in FIG. 28 are stored in memory, then the control of the support frame 75 is initiated with such output values as the target values, and the support frame 75 is moved within a one second period to the predetermined target values at the optical center (see 75g in FIG. 28).
After the locking ring 719 is rotated to the unlocked state, the support frame 75 is driven based on the target values from the vibration detection means (in superposition with the above-mentioned movement of the support frame 75 to the central position), whereby a vibration prevention operation is initiated.
When the vibration prevention operation is turned off at 719j, the target values from the vibration detection means are no longer entered into the correction drive means for driving the correction means, whereby the support frame 75 is controlled and stopped at the central position. In this state, the attracting coil 730 is deactivated (730b), whereby the attracting yoke 729 loses the attracting force to the armature 724 and the locking ring 719 rotates clockwise under the force of the locking spring 728 and returns to the state shown in FIG. 27A. In this state, the locking ring 719 impinges on the locking rubber 726, thus being restricted in rotation, whereby the noise of collision of the locking ring 719 at the end of rotation can be suppressed.
Thereafter (for example after 20 msec), the control of the correcting drive means is terminated, whereby the control shown in FIG. 28 is terminated.
FIG. 29 is a block diagram showing a circuit configuration relating to the image blur correcting function, in a camera provided with the above-explained image vibration correcting device.
The output of vibration detection means 2 is amplified by amplifier means 3, and is entered into an A/D conversion port of a microcomputer. Also the output of position detection means 4, for detecting the position of the correction lens, is amplified by amplifier means 5 and entered into the A/D conversion port of the microcomputer 1. The microcomputer 1 processes these two signals and outputs correction lens driving data to correction lens drive means 6, thereby driving the correction lens and correcting the image blur. Lock-unlock drive means 7 executes the drive for the aforementioned locking coil, to maintain the device in the unlocked state.
In the following there will be explained an example of the functions of the microcomputer 1 relating to the image blur correcting device, with reference to a flow chart shown in FIG. 30.
The correction of image blur is executed by an interrupt process, for example, at a predetermined timing interval. The aforementioned lock-unlock control is executed in a main flow of the camera.
In response to an interrupt signal, the microcomputer 1 starts the sequence from a step #81:
[step #81] executes A/D conversion of the output of the vibration detection means 2 composed, for example, of an angular velocity sensor; PA1 [step #82] discriminates whether an image blur correction start command has been received, and, if not, the sequence proceeds to a step #83. PA1 [step #83] initializes the DC offset and the integration calculation, as the image blur correction is not executed; PA1 [step #84] clears a timer for measuring the time after reception of the image blur correction start command. PA1 [step #85] discriminates whether a predetermined time has elapsed since the reception of the image blur correction start command, and, if not, the sequence proceeds to a step #86. PA1 [step #86] calculates the DC offset, in order that the initial input to the high-pass filter does not show an abrupt change (or a stepped input) by the DC component; PA1 [step #87] initializes the high-pass filter calculation, thereby bringing the result of integration to 0, in order to electrically retain the correction lens at the center. PA1 [step #88] cuts off the components under a predetermined frequency (cut-off frequency determined by capacitor and resistor) from the A/D converted output of the angular velocity sensor, in order to initiate the image blur correction, and executes a high-pass filter calculation for passing the signal components of actual vibration; PA1 [step #89] executes a known integration for calculating the angular displacement data; PA1 [step #90] executes an adjustment for the variation in the amount of eccentricity (sensitivity) of the correction lens relative to the vibration angle, depending on the zoom or focus position; PA1 [step #91] stores the result of the abovementioned calculation (drive data for image blur correction) in a RAM area set by SFTDRV in the microcomputer 1; PA1 [step #92] discriminates whether the correction system driving data SFTDRV is within the electrically movable range (stroke limit position) DRVLMT, and, if within that range, the sequence proceeds to a step #94; if not within the range, the sequence proceeds to a step #93; PA1 [step #93] writes, as the correction system driving data SFTDRV exceeds the stroke limit position DRVLMT, the value of the stroke limit position DRVLMT as the correction system driving data SFTDRV; PA1 [step #94] executes A/D conversion on the output of the position detection means 4, detecting the position of the correction lens, and stores the obtained result in an area SFTPST of the RAM; PA1 [step #95] executes a feedback calculation (SFTDRV-SFTPST); PA1 [step #96] multiplies the result of the feedback calculation with the loop gain; PA1 [step #97] executes a phase compensation calculation for realizing a stable control system; PA1 [step #98] outputs the result of the phase compensation calculation by a PWM signal to the port of the microcomputer 1, whereupon the interrupt process is terminated.
Steps #83 and #84 are operations without the image blur correction:
If the foregoing step #82 identifies that the image blur correction start command has been received, the sequence proceeds to a step #85:
Steps #86 and #87 are operations within a predetermined time after the reception of the image blur correction start command, during which the image blur correcting operation is not yet executed:
If step #85 identifies the lapse of the predetermined time after the reception of the image blur correction starting command, the image blur correcting operation is initiated from a step #88:
The above-mentioned output is supplied to the correction lens driving means 6, thereby driving the correction lens and correcting the image blur.
In this manner image blur correction is conducted by the above-explained configuration.
In a camera equipped with the above-explained image blur correcting device, the actual photograph taking operation is conducted not only for a still object but also by following a moving object or by changing the aimed object, and the panning operation is frequently employed in such photograph taking operation.
Also the photographer may intentionally produce a vibration larger than hand vibration, in order to confirm, on the view finder, that the image blur correction function is properly functioning.
In such a panning operation, a signal of a large amplitude is entered into the angular velocity sensor, and, if the image blur correction is executed according to such signal, the correction lens collides with the mechanical stroke end (end of mechanically movable range) eventually resulting in generation of noise or damage in the correction lens. In order to prevent such situation, there has been adopted a countermeasure such as varying the characteristics of integration for a vibration of a large amplitude or setting an electrical stroke limit position as explained in the foregoing steps #92 and #93.
However, in case a large vibration is intentionally given in the direction of gravity, the correction lens cannot stop at the electrical stroke limit position because of the weight of the correction lens and the inertial force thereof but may collide with the mechanical stroke end beyond the electrical stroke end, thus leading to noise generation and damage of the correction lens. Such possibility increases particularly in a case where the correction lens becomes heavier, with correspondingly increased gravity and inertial force.
In order to prevent such situation, it is conceivable to select a smaller electrical stroke limit position. However, since the electrical stroke limit position is the same in the vertical (gravitational) direction and in the horizontal (perpendicular) direction, such selection leads to a general contraction of the stroke range. Though the range of correction can theoretically be selected larger in the horizontal direction because the possibility of going beyond the limit position and colliding with the mechanical stroke end is low due to the absence of a gravitational force, it has not been possible to select an effective stroke for the above-mentioned reason.
Also the precision of the image blur correction can be improved by optimizing the control according to the various situations, such as photographing of a still object, photographing of a moving object and photographing with the camera installed on a tripod.
For this reason, it has already been proposed to provide plural image blur correction modes and to effect optimum control of image blur correction according to the selected mode, thereby improving the precision of the image blur correction.
In such system, there should be an optimum range enabling the image blur correction in each mode, but such difference has not been considered and the image blur correcting range has been selected to be the same in all the modes.
Also, in a camera equipped with the above-explained image blur correcting device, there exists image blur correcting characteristics for matching each of various situations, such as photographing of a still object, photographing of a moving object and photographing with the camera installed on a tripod, and it is important to suitably select such characteristics.
For example, in the case of photographing a still object, there can be selected such image blur correcting characteristics as to correct even vibration of a low frequency, but, in the case of photographing a moving object, the image blur correction with such characteristics will respond also to a panning operation, so that the operability of the camera will be deteriorated. In such case, therefore, the characteristics covering the low-frequency range should be eliminated.
For this reason, it has already been proposed to provide plural image blur correction modes and to effect optimum control of the image blur correction operation according to the mode selected by an external operation, thereby enabling optimum photographing operation under any photographing situation.
However, if the image blur correction mode is switched in the course of the image blur correcting operation, the characteristics change totally so that the result of calculation of the vibration detection shows a discontinuous change. As the image blur correction is executed according to such calculations, an abrupt change will occur in the image in the view finder, resulting in an unpleasant feeling for the photographer.